Detergent tablet of amorphous sodium silicate having inherent binding properties,containing a surfactant,and method of making such tablet

ABSTRACT

Amorphous sodium silicate having a burr-like structure imparting inherent binding properties thereto, is compressed into detergent tablets which contain a surfactant.

Tl ited States Patent Gaiser 1 *July 4,1972

[54] DETERGENT TABLET OF AMORPHOUS SODIUM SILICATE HAVING INHERENT BINDING PROPERTIES, CONTAINING A SURF ACTANT, AND METHOD 0 MAKING SUCH TABLET [72] Inventor: Conrad J. Gaiser, 24 66th Place, Long Beach, Calif. 90803 Notice: The portion of the term of this patent subsequent to June 17, 1986, has been disclaimed.

[22] Filed: April 14, 1969 211' Appl. No.: 815,990

Related US. Application Data [63] Continuation-in-part of Ser. No. 654,230, July 18,

1967, Pat. No. 3,450,494, which is a continuation-inpart of Ser. No. 352,142, March 16, 1964, abandoned.

[52] U.S.Cl ..252/135,252/527,252/539, 252/DIG. l6

[51] 1nt.C| ..Cl1d7/l4,C11d7/48,C11d 17/00 [58] Field ofSearch ..252/l02,135, 137, 138

[5 6] References Cited UNITED STATES PATENTS 3,450,494 6/1969 Gaiser ..252/133 X 3,318,817 5/1967 Smith ..252/l37 3,247,122 4/1966 Schaafsma et al. ..252/135 Primary Examiner-Leon D. Rosdol Assistant ExaminerDennis L. Albrecht AttarneyStanley Bialos [5 7] ABSTRACT Amorphous sodium silicate having a burr-like structure imparting inherent binding properties thereto, is compressed into detergent tablets which contain a surfactant.

8 Claims, 3 Drawing Figures DETERGENT TABLET OF AMORPHOUS SODIUM SILICATE HAVING INHERENT BINDING PROPERTIES, CONTAINING A SURFACTANT, AND METHOD OF MAKING SUCH TABLET REFERENCE TO COPENDING APPLICATION The instant application is a divisional continuation-in-part of applicant's allowed copending application, Ser. No. 654,230, filed July 18, 1967, for Amorphous Sodium Silicate Having Inherent Binding Properties, and Method of Producing Same, now U.S. Pat. No. 3,450,494, dated June 17, 1969 which in turn was a continuationin-part of applicants now abandoned parent application, Ser. No. 352,142, filed Mar. 16, 1964.

This invention concerns sodium silicate, and more particularly novel amorphous sodium silicate having inherent binding properties, and which is compressed into a tablet containing a surfactant.

Because of their desirable soil removal and soil suspending properties, sodium silicates are widely employed in laundering products. The alkalinity imparted by the sodium oxide component fulfills many functions. It serves to neutralize acids, saponify fats or oils, and enhance the detersiveness of soaps and other surfactants, such as alkyl aryl sulfonates and nonionic detergents, which are formed or added. The silica component serves to suspend removed soil, preventing redeposition.

As is well known, the sodium oxide (Na O) to silicon dioxide (SiO ratio varies widely in the various sodium silicates. Sodium metasilicate has a mol ratio of Na O to SiO of l to 1; sodium sesquisilicate, a mol ratio of l to 0.67 and sodium orthosilicate, a mol ratio of l to 0.5. The latter, because of its high alkali to silica mol ratio is commonly employed for commercial laundering. Heretofore, all these sodium silicates have been of crystalline nature.

Even at elevated temperatures, crystalline sodium orthosilicate is only slowly solubilized in water, and much of the orthosilicate is not available as a colloid to provide soil suspension. Similarly, the crystalline metaand sesquisilicates are even more slowly solubilized, suffering from the same disadvantages as the orthosilicate.

This invention has as its objects, among others, the preparation of a novel physical form of sodium silicate which is rapidly dispersible in water to form highly colloidal solutions having improved soil suspension properties, namely, burr-like, spongy amorphous sodium silicates of varying Na O to SiO mol ratios, and compressed masses of said sodium silicate, particularly in the form of tablets containing a surfactant.

The burr-like, spongy amorphous sodium silicates prepared by the process of this invention have excellent inherent binding properties to form integral masses when compressed, such as tablets and briquettes without requiring extraneous binders or the removal of moisture by heat or other extraneous means. It has other valuable physical characteristics, particularly light density suitable for insulation purposes, not typical of crystalline sodium silicates.

Other objects of the invention will become apparent from the following description, and drawing in which:

FIG. 1 is a schematic view of a form of apparatus for forming the amorphous sodium silicate hereof;

FIG. 2 is a pictorial cross-sectional view magnified about times, illustrating a spongy, burr-like particle of the product hereof; and

FIG. 3 is a similar view of a sodium silicate particle resulting from spray drying.

According to this invention and as is disclosed in the aforementioned US Pat. No. 3,450,494, some of the water in an aqueous liquid dispersion or suspension of sodium silicate in which the water is superheated, is flashed off at an elevated temperature, by forcing such heated dispersion from a zone of relatively high pressure into a static unheated expansion zone of relatively low pressure. The flashing off of the water is effected so rapidly without application of heat that the resultant sodium silicate droplets thus formed have insufficient time to crystallize while expanding to burr-like, spongy masses, and instantly cool to amorphous state.

The released water vapor is simultaneously vented, and solid amorphous free-flowing sodium silicate particles are formed and collected without further application of heat or drying by heated gas or air. If spray drying were employed by application of external heat, the particles would pop open, thus losing their binding properties. In this connection, it is only necessary to flash ofi sufficient water so that the resultant spongy, burr-like particles are solids at ambient temperatures and pressures.

FIG. 2 illustrates pictorially the burr-like, spongy character of a particle of sodium silicate resulting from the method hereof. It has projecting spurs 2 which form an irregular outline, and minute voids 2 which impart sponginess. The surface is not glazed or glassy which would otherwise result from application of heat, as in spray drying. Thus, when a multiplicity of particles are compressed together, the burrs enhance binding for formation of pellets or briquettes. In contradistinction, as shown in FIG. 3, a spray dried particle is substantially a hollow sphere with an opening 3 through which steam has escaped. The outer shell surface 4 of the sphere is hardened and glazed, and much harder than the inner surface 5. Compression on a plurality of particles results in crushing to a fine dense powder having no inherent binding properties.

The sodium silicate employed in the dispersion may be preformed sodium silicate, or may be formed in situ from the components which make up sodium silicate, namely, sodium oxide and silicon dioxide. Hence, sodium silicate referred to herein is meant to include both sources.

For most advantageous uses, the amorphous sodium silicates of this invention have mol ratio ranges of sodium oxide (Na O) to silicon dioxide (SiO of about I to 0.5, to l to 5.0. By varying the ratios of the Na O to SiO the products have different properties which make them applicable for a variety of uses. Ratios of Na O to SiO of l to 2, to l to 3 are advantageous for domestic laundering uses. Decreasing the amount of Na O so that the mol ratio of Na O to SiO is substantially less than I to 3 provides products having good insulating properties. Preferred mol ratio ranges of Na O to SiO are l to 0.5, to l to 3 for domestic and commercial laundering uses, while 1 to 3, to l to 5.0 for insulation purposes. However, the method of this invention is not dependent on the molar ratios of Na O to SiO as various well known ratios can be employed to produce the burr-like spongy amorphous sodium silicate.

The physical properties of the amorphous sodium silicates hereof may be varied by the amount of water contained therein. Usually the weight percent of water will be in the range of 15 to 30, more usually in the range of 18 to 26. Increasing amounts of water result in lower melting points, greater plasticity and greater rates of solubility, while decreasing amounts of water result in higher melting points, less plasticity, and rapidly decreasing solubility.

As previously mentioned, the particles as prepared are noncrystalline, and appear as having a rugged burr-like nature. They generally range from 5 to mesh size, more usually from 10 to 20 mesh size.

The bulk density of the novel amorphous particles, namely, the density of a mass of particles as formed, is usually in the range of 8 to 35 lbs./ft. more usually in the range of 15 to 21 lbs/ft. Such density is determined by the amount of water originally present, the amount of water flashed off, and the amount of water remaining. Under any given conditions, the more water flashed off, the lower will be the bulk density. The bulk densities of crystalline sodium silicates are in the range of 75 to 150 lbs/ft. The amorphous particles hereof may, however, be compacted under pressure in conventional briquette or tablet forming apparatus to solid masses having densities as high as 65 lbs./ft. or even greater. They may also be expanded to spongy substantially anhydrous masses, by quick heating to an elevated temperature, to provide particles suitable for insulation purposes.

As already stated, the novel burr-like, spongy amorphous sodium silicate particles of this invention are prepared by the rapid flashing off of water without application of heat, from an aqueous dispersion of sodium silicate while simultaneously venting off the flashed water. This is desirably done by ejecting the heated aqueous dispersion wherein the water is superheated and in liquid phase, at a relatively high temperature and pressure into an unheated expansion zone of much lower pressure, thus creating a pressure drop. The pressure drop will usually be at least about 500 p.s.i. As a result, the particles formed are cooled so fast below their melting points as to preclude crystal formation and form the burr-like, spongy, amorphous particles.

The process will be further described with the aid of the accompanying drawing which illustrates schematically a form of apparatus for continuously effecting the temperature and pressure drop. Various materials, namely, aqueous sodium silicate, water, sodium hydroxide, and a minor amount of the usual laundering additives if desired, such as borax, phosphates, brighteners or the like, as explained hereinafter, are introduced into a vessel which is shown open but may be closed, provided with an agitator 12, drain l3, and outlet 14. The various components are continuously stirred to insure thorough mixing into a uniform slurry or dispersion, and then pumped under pressure by pump through conduits 16 and 17 into a suitable heat exchanger 18, which may be of the electrical type having electrical heating means 18.

After being heated to the desired temperature, the dispersion from heat exchanger 18 passes from the heat exchanger through conduit 19, manually operable flow regulator valve 20 controlling the rate at which the dispersion is fed, and conduit 21, and is then released by ejecting through restricted orifice or nozzle 22 into expansion vessel 23, maintained at a sufficiently lower pressure at ambient temperature than that of the dispersion introduced. Nozzle 22 is preferably not a multiorifice spray head but is desirably a simple orifice nozzle. Also, the atmosphere in expansion zone 23 is static in that a moving column of gas is not required to effect extraneous drying of the resultant particles.

Substantially all moisture loss is effected by the flashing off of the water; and the water vapor produced is vented to the atmosphere through vent 24, while the dry, burr-like spongy amorphous sodium silicate particles are collected by screw conveyor 25 which conveys such particles to be packaged or used in any desired way. Because loss of water is effected solely by flash-ofl in expansion chamber 23, a tower is not required as in spray drying.

The temperature of the heat exchanger 18 need only be high enough to solubilize the sodium silicate dispersion or suspension fed in, and provide a homogeneous colloidal solution in which substantially all of the sodium silicate is uniformly dispersed, and to impart sufiicient heat to the solubilized dispersion to flash off water when the solubilized dispersion is released into the lower unheated pressure zone 23 which is desirably at atmospheric pressure. As previously related, the pressure maintained by pump 15 throughout the system up to the discharge nozzle 22, is such as to maintain substantially all the water in the dispersion in the liquid phase.

To produce the burr-like, spongy sodium silicate by the aforementioned water flash-off method, the aqueous sodium silicate fed into the system must initially be a dispersion or slurry. Such dispersion should usually have 45 to 80 weight percent of sodium silicate or components which form the same, and desirably 50 to 75 weight percent to insure a dispersion because by the method hereof release of water is effected solely by flash-off of the water, and generally less than 50 percent water by weight of the original water content of the sodium silicate dispersion can be flashed off at one time in the expansion chamber. Hence, if the initial water content of the aqueous sodium silicate is such that a solution is initially fed into the system, the original water content will be too high and consequently not enough water can be flashed off at one time to fonTl particles.

Generally, the temperatures used are in the range of about to 358 C.; the latter temperature being the highest at which water will remain in the liquid phase at any pressure. More particularly, the temperature is in the range of about to C. The pressure, which must be at least sufficient to maintain the water in the liquid phase, will generally be in the range of about 500 to 5,000 p.s.i. more usually, in the range of 1,000 to 3,000 p.s.i.

The pressure in the expansion vessel need only be substantially lower than the pressure at which the aqueous sodium sil icate solution is sprayed. Usually, the pressure will vary from atmospheric to 5 atmospheres; preferably the pressure will be 1 atmosphere (about 15 p.s.i.). Although the particular pressure is not critical, it should be low enough to allow the water to flash off or vaporize substantially instantaneously. In some instances, it may be advantageous to use sub-atmospheric pressures, in order to release the aqueous sodium silicate solution at a lower pressure and temperature. The time for which the reaction mixture is heated at the elevated pressure is generally in the range of 0.25 to 5 minutes, more usually in the range of 0.5 to 2 minutes.

The orifice size will be governed by the size of the equipment, the pressure differential, the rate of production of the amorphous sodium silicate, etc. The orifice size chosen will not only govern the rate at which the material can be processed, but also the size of the burr-like, spongy sodium silicate particles, assuming the other variables are held constant.

In some instances, the product may still contain too much water and appear gel-like and plastic at room temperature. If so, the product may then be again superheated at a suitable temperature and pressure to provide a pumpable dispersion which may be again released into the expansion zone in the manner described to effect further flashing off of water, providing a final amorphous product having a desired water content.

When fonning the initial liquid dispersion, various sources of dry and liquid sodium silicates or components which form the same, may be used. An increase in the mol ratio of Na O to Si0 can be obtained by using caustic soda (NaDH). The amount of water may be adjusted by the addition of water and the choice of the sodium silicate concentration. Commercial sources of sodium silicate are available which have mol ratios of Na O to SiO as high in SiO as l to 3.75.

As previously indicated, additives may be included with the aqueous sodium silicate dispersion, which are stable under the conditions of the process. Various well known additives, such as phosphates, borates, salts, clays or the like, can be included with the other materials in the aqueous sodium silicate dispersion so as to be incorporated in the final solid product.

While the invention is not to be limited to the following theoretical description, the process is considered to operate in the following manner. As the superheated solubilized aqueous dispersion discharges through the release orifice 22 from a zone of high pressure to one of lower pressure, a portion of the water contained, flashes to vapor. The rapid flash evaporation of the water and the subsequent rapid cooling of the solids do not provide sufficient time for the sodium silicate to crystallize, resulting in burr-like, spongy amorphous particles of a wide range of bulk densities and particle size. In all cases, the particles are non-crystalline amorphous, supercooled particles associated with the remaining unevaporated water.

The following examples will serve to further illustrate the invention; the resultant products being all suitable for soil suspension in laundering.

EXAMPLE 1 Into vessel 10 was introduced 49.87 parts by weight of commercial Calquartz SS-65" sodium silicate powder by Philadelphia Quartz Company, (the Na O, SiO and H 0 content being 23.l, 74.4, 2.5 weight percent, respectively); 49.43 parts by weight of 50 weight percent aqueous caustic soda (NaOH); and 9.5 parts by weight of anhydrous caustic soda.

The mixture was heated to 154 C. in heat exchanger 18, maintained at that temperature for a residence time of one minute at 1,500 p.s.i. pressure until it reached nozzle 22, and then released through a 3/64-inch orifice into unheated expansion zone 23 maintained at atmospheric pressure and ambient temperature. The product was solid amorphous sodium silicate of a bulk density of about 16 lbs. per cubic foot, having a water content of about 22.5 weight percent, and a Na O to SiO mol ratio of about 1 to 1.

EXAMPLE [I lnto vessel 10, as in Example I, was introduced 100 parts of a 35 Baume solution of commercial Calquartz S-35 by Philadelphia Quartz (Na O to SiO ratio being I to 3.75) which was heated to 165 C., maintained at that temperature for 1 minute at 1,500 p.s.i. pressure, and then released as described in Example I. The product was barely a plastic gel at room temperature having about 35 percent water content by weight. The product was put through the process under the same conditions as in the first pass, reducing the water content to about 22 percent by weight. The particles had a mol ratio of Na O to Si0 of l to 3.75, and were lightweight granular, slowly water-soluble and free flowing, of a bulk density of about 20 lbs. per cubic foot.

When heated quickly to 350 F., the particles expanded into spongy masses of an anhydrous nature of a bulk density of 2 lbs. per cubic foot, which had valuable insulating properties.

EXAMPLE lll Into the vessel was introduced 45 parts of commercial N Brand" liquid by Philadelphia Quartz, (38 weight percent aqueous sodium silicate, Na O to SiO being I to 3.2); 35 parts dry sodium silicate powder (Na O to SiO being 1 to 3.2); 20 parts of 50 weight percent aqueous caustic soda; and parts of trisodium phosphate (Na PO '5l-l O). The mixture was heated for about 1 minute at 165 C. under 1,500 p.s.i. pressure and then released through a 3/64-inch diameter orifice to atmospheric pressure at ambient temperature. The product had about 25 weight percent water and a Na O to SiO mol ratio of l to 2.6. The bulk density was about 12 lbs. per cubic foot.

As previously indicated, particularly advantageous because of its inherent or self-binding properties under compression, are compressed tablets of the amorphous sodium silicate hereof containing a surfactant, and which are free of other binding material. It is desirable to employ a liquid surfactant or waxy material which melts to a liquid mass, and to effect absorption of the surfactant into a compressed tablet either by spraying the liquid onto the surfaces of the tablet or by impregnating the tablet by immersion in a bath of the liquid surfactant. By such application, the surfactant is absorbed near the surfaces of the tablet being concentrated in about the first three-sixteenths of an inch near the surface, thus protecting the tablet from absorbing carbon dioxide from the atmosphere during storage of the tablet. Also, because of being near the surface, the surfactant becomes readily available in the wash water.

However, the surfactant may be in powder form and compressed together with the amorphous sodium silicate to form a tablet but then the surface protection and availability of the surfactant is not as effective. Part of the surfactant may be in powder form and compressed together with the amorphous sodium silicate, and the remainder of the surfactant absorbed into the tablet in liquid form. Desirably, the amount of liquid surfactant should be at least about 20 percent by weight of the total amount of surfactant.

It is relatively immaterial how much liquid surfactant is absorbed, as excesses do no harm but are not economical. Suitable pressures for making tablets are about 10 to 80 lbs. per square inch, to produce tablets having a bulk density of about 20 to 80 lbs. per cubic foot. The following are typical examples of tablets containing a surfactant.

EXAMPLE A About 91 percent by weight of the product from Example Ill (25 percent moisture, Na O to SiO of l to 2.6 mol ratio) was blended with 8 percent by weight of a suitable surfactant, namely, nonylphenol to which 9.5 mols of ethylene oxide had been added, add 1 percent by weight of a conventional mixture of perfumes, optical brighteners and carboxymethylcellulose. When the mixture was compressed in a conventional briquette forming press, into briquettes (3 inches in diameter and 1 inch thick) to a bulk density of about 50 lbs. per cubic foot, a stable rugged non-crumbling tablet was obtained in which the mass was adhesively bonded by virtue of the inherent binding properties of the amorphous sodium silicate. Yet, the tablet was rapidly soluble in water and had cleaning characteristics comparable to compositions using surfactants and phosphate.

Moreover, mixtures containing as low as 20 percent by weight of the sodium silicate product of Example lII formed suitable detergent tablets bound together by the amorphous sodium silicate, when blended with percent by weight of conventional laundering additives.

EXAMPLE B The following two examples show widely varying detergent compositions utilizing the novel amorphous sodium silicate of this invention. Laundry detergenttablets were prepared having the following composition:

Weight Percent a. Amorphous sodium silicate (Na O to SiO.;; 1 to 2.6; 25 weight percent H 0) 81 Dodecyl benzene sulfonate-sodium salt (solid anionic surfactant) 18 Optical brightener Blancophor DS) 0.01 Perfume (Florosynth Lab's Honeysuckle 0.49 *Carboxymethylcellulose (thickener) 0.50 b. Amorphous sodium silicate (Na O to SiO,; 1 to 2.6; 25 weight percent H O) 23.5 Sodium polypropylene benzene sulfonatc (solid surfactant) 15.0 Sodium tripolyphosphate 40.0 Soda Ash 20.0 Optical brightener (Blancophor DS) 0.01 Perfume (Florosynth Labs Honeysuckle 90) 0.49 Carboxymethylcellulose 1.00

*Optional In equipment regularly used to produce tablets, each of these compositions was formed into tablets useful as premeasured laundry detergents. Tablet formation was easier than with most powders, as little or no lubricant was needed. The tablets formed were unusually resistant to mechanical damage, and could be handled with the usual packaging equipment without difiiculty.

Another method of producing a useful tablet employing the novel amorphous sodium silicate is to compress a mixture similar to those described above, but omitting the solid surfactant. The tablet is immersed in a suitable liquid non-ionic surfactant, such as nonylphenoxy polyethylene oxide, until the desired weight of the surfactant is absorbed, usually about 4 to 15 percent by weight, preferably about 6 to 8 percent. A surfactant of suitable properties will absorb near the surface where it will reinforce and protect the structure of the tablet and be more rapidly solubilized into the use solution than is the rest of the tablet, a sequence of application which promotes good laundering.

A tablet is formed which does not require wrapping and is readily dispensed from automatic vending devices. Other types of well known surfactants for imparting detersiveness to the tablets can be incorporated therein in the same manner, as

EXAMPLE The amorphous sodium silicates are also useful for dishwashing tablets. This use is exemplified by a tablet having the following composition: 98 parts amorphous sodium silicate (Na O to SiO of l to 2.6 mol ratio, 25 weight percent water), 1 part trisodium ethylene diamine tetraacetic acid (sequestering agent), and 1 part Surfonic LF-7 (Jefferson Chemical Companys low foam non-ionic surfactant). Thisproduct was used in a home dishwasher, one tablet weighing 8 grams being used each load. Excellent results were consistently obtained.

It is evident from the foregoing examples that the amorphous sodium silicates of this invention can be combined with a wide variety of surfactants to produce valuable laundering and dishwashing powders, and also tablets. These amorphous sodium silicates have particularly desirable properties of binding together surfactants and other conventional laundry or dishwashing compound ingredients to form stable, rugged masses wherein the amorphous sodium silicate will rapidly dissolve in water and provide superior soil suspension properties. With molar ratios of SiO to Na O greater than 3 to I good insulating materials are obtained.

In addition to the surfactants set forth in the foregoing examples, other typical surfactants that can be employed usually in an amount of about 4 to percent by weight, as previously mentioned, although such proportions are not critical, are linear alkyl sulfonate, sodium salt (Calsoft LAS-99 by Pilot Chemicals), ethoxylated linear alcohols (Tergitol S by Union Carbide), and ethoxylated alkyl phenols (Triton X-lOO by Rohm and Haas Co.). In this connection, any suitable surfactant can be employed which will protect the surface of the tablet, and also enhance solubilization thereof into the use solution.

I claim:

1. A solid detergent tablet comprising (A) a compressed mass of non-crystalline, amorphous, burr-like, spongy sodium silicate particles having a bulk density of about 8 to 35 lbs. per cubic foot and having the property of forming a highly colloidal dispersion in water to provide effective soil suspension, said sodium silicate particles being obtained by heating under a pressure of at least 500 lbs. per square inch an aqueous sodium silicate liquid dispersion having a sodium silicate content of about 45 to 80 percent by weight, and substantially instantaneously flashing off water therefrom by forcing such heated liquid under pressure into an expansion zone of a lower pressure of at least about 500 lbs. per square inch and at ambient temperature and in the absence of a moving column of air while simultaneously allowing rapid cooling of the particles, and (B) a detersiveness imparting surfactant bound in said mass of compressed particles in an amount effective to protect the surface of the tablet and enhance solubilization of said tablet into an aqueous use solution, the amount of said amorphous sodium silicate being at least about 20 percent by weight of the tablet effective to form a colloidal solution in said use solution and suspend soil.

2. The tablet of claim 1 wherein said surfactant is a liquid absorbed in said mass.

3. The tablet of claim 2 wherein said liquid surfactant provides a protective layer at the surfaces of said tablet.

4. The detergent tablet of claim 1 free of other binding material. I

5. The detergent tablet of claim 1 in which the amount of surfactant is about 4 to 15 percent by weight of the tablet.

6. The method of making a solid detergent tablet of noncrystalline, amorphous, burr-like, spongy sodium silicate particles having inherent binding properties and a bulk density of about 8 to 35 lbs. per cubic foot and having the property of forming a highly colloidal dispersion in water to provide effective soil suspension, said sodium silicate particles being obtained by heating under a pressure of at least about 500 lbs. per square inch an aqueous sodium silicate liquid dispersion having a sodium silicate content of about 45 to percent by weight, and substantially instantaneously flashing off water therefrom by forcing such heated liquid under pressure into an expansion zone of a lower pressure of at least about 500 lbs.

per square inch and at ambient temperature and in the absence of a moving column of air while simultaneously allowing rapid cooling of the particles; said method comprising compressing such particles to a solid mass to bind said particles together by their inherent binding properties, and contacting said solid compressed mass with a liquid detersiveness imparting surfactant to impregnate said mass with said surfactant, the surfactant being in an amount effective to protect the surface of the tablet and enhance solubilization of said tablet into an aqueous use solution, and the amount of said amorphous sodium silicate particles being at least about 20 percent by weight of the tablet effective to form a colloidal solution in said use solution and suspend soil.

7. The method of claim 6 wherein such impregnating is effected by immersion of said solid mass in said liquid surfactant.

8. The method of claim 6 wherein such impregnating is effected by spraying said liquid surfactant onto said solid mass. 

2. The tablet of claim 1 wherein said surfactant is a liquid absorbed in said mass.
 3. The tablet of claim 2 wherein said liquid surfactant provides a protective layer at the surfaces of said tablet.
 4. The detergent tablet of claim 1 free of other binding material.
 5. The detergent tablet of claim 1 in which the amount of surfactant is about 4 to 15 percent by weight of the tablet.
 6. The method of making a solid detergent tablet of non-crystalline, amorphous, burr-like, spongy sodium silicate particles having inherent binding properties and a bulk density of about 8 to 35 lbs. per cubic foot and having the property of forming a highly colloidal dispersion in water to provide effective soil suspension, said sodium silicate particles being obtained by heating under a pressure of at least about 500 lbs. per square inch an aqueous sodium silicate liquid dispersion having a sodium silicate content of about 45 to 80 percent by weight, and substantially instantaneously flashing off water therefrom by forcing such heated liquid under pressure into an expansion zone of a lower pressure of at least about 500 lbs. per square inch and at ambient temperature and in the absence of a moving column of air while simultaneously allowing rapid cooling of the particles; said method comprising compressing such particles to a solid mass to bind said particles together by their inherent binding properties, and contacting said solid compressed mass with a liquid detersiveness imparting surfactant to impregnate said mass with said surfactant, the surfactant being in an amount effective to protect the surface of the tablet and enhance solubilization of said tablet into an aqueous use solution, and the amount of said amorphous sodium silicate particles being at least about 20 percent by weight of the tablet effective to form a colloidal solution in said use solution and suspend soil.
 7. The method of claim 6 wherein such impregnating Is effected by immersion of said solid mass in said liquid surfactant.
 8. The method of claim 6 wherein such impregnating is effected by spraying said liquid surfactant onto said solid mass. 